The present invention relates to the use of transition metal complexes as means to store information in optical information storage devices.
Great interest is currently devoted to bistable molecular or supramolecular species presenting two forms whose interconversion can be modulated by an external stimulus. (Lehn J.-M., Supramolecular Chemistry, Concepts and Perspectives; VCH: Weiheim, (1995)). The design of such molecular-level switching devices is directly linked to the chemistry of signal generation, transfer, conversion, storage and detection.
Typical bistable species include photochromic compounds, which are molecules that can be interconverted between two forms exhibiting different visible light absorption (i.e., color). Photochromism occurs in a wide variety of materials, including both inorganic and organic compounds. Illustrative of the classes of organic compounds are anils, disulfoxides, hydrazones, oxazones, semicarbazones, stilbene derivatives, succinic anhydrides, camphor derivatives, syndromes and spiro compounds. A rather large variety of inorganic compounds show photochromism, including metal oxides, alkaline earth metal sulfides, titanates, mercury compounds, and copper compounds. These materials have been known for a long time and a description of these systems can be found in the literature. (xe2x80x9cPhotochromismxe2x80x9d Glenn H. Brown Ed., Volume III, John Wiley and Sons, Publisher, 1971).
Because they interconvert between two different colors, photochromic compounds have the capability to function as a binary information storage system. One color represents 0, and the second color 1, to encode information in digital format. Molecular level optical memory devices incorporating these molecules should offer the possibility of packing an extremely large quantity of information into a small space, which can be read through a binary code with a resolution of the order of nanometers.
However, previously known photochromic compounds are unsuitable for long term information storage applications. Most photochromic compounds change their color by photoexcitation and revert, more or less slowly, to their initial state when kept in the dark. Compounds exhibiting this behavior are useless for information storage since the written information is spontaneously erased after a relatively short time.
Other prior photochromic compounds are more stable, but tend to undergo reversible photoisomerization. (Irie, M.; Mohri, M. J. Org. Chem. 53, 803 (1988); Hanazawa, M; Sumiya, R.; Horikawa, Y.; Irie, M; J. Chem. Soc. Chem. Commun. 206 (1992); Saika, T; Irie, M; Shimidzu, T; J. Chem. Soc. Chem. Commun. 2123 (1994)). Such compounds can be used for information storage optoelectronic devices, but do not provide a good long term storage solution, because the light used for reading the written data causes the back-conversion of the sampled molecules, and thus the gradual loss of information. Several attempts have been made to overcome this difficulty, including the use of photochemically inactive infrared light to read the status of the system.
Consequently, there is a need for improved photochromic molecules which will provide for stable, long-term storage of information.
The present invention overcomes the shortcomings of the prior art photochromic molecules by providing reactive species which undergo stable and irreversible color changes under controlled conditions.
In one aspect of the invention, a binary data recording medium is provided which includes a substrate and a recording layer on the substrate. The recording layer includes an organometallic transition metal complex which absorbs at a first wavelength. When the complex is subject to a light-induced excited state resulting in a reaction product in the recording layer, it absorbs light having a second, different wavelength. The light absorption of the first wavelength is assigned a first value, and light absorption of the second wavelength is assigned a second value, the first and second values corresponding to binary code.
The transition metal complex in one aspect of the present invention includes at least one of the following formulas: [M(Nxe2x80x94N)2L2]n, [M(Nxe2x80x94N)L4]n, [M(Nxe2x80x94Nxe2x80x94N)L3]n, and [M(Nxe2x80x94Nxe2x80x94N)2]n. M is a transition metal; Nxe2x80x94N is a chromophoric polypyridine ligand incorporating from one to two substituents selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, and xe2x80x94Rxe2x80x94PO3H2, where R is a saturated or aromatic hydrocarbon group; Nxe2x80x94Nxe2x80x94N is a chromophoric terpyridyl ligand incorporating from one to three substituents selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, xe2x80x94Rxe2x80x94PO3H2, and phenyl, where the phenyl incorporates one or more substituents selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, xe2x80x94Rxe2x80x94PO3H2, where R is a saturated or aromatic hydrocarbon group; and L is a nonchromophoric monodentate or polydentate ancillary ligand.
In other aspects of this particular embodiment, M is selected from cobalt, nickel, copper, iridium, palladium, platinum, rhenium, osmium, iron, ruthenium and rhodium; Nxe2x80x94N is selected from substituted and unsubstituted 2,2xe2x80x2-bipyridyl, substituted and unsubstituted 1,10-phenanthroline and substituted or unsubstituted 2,2xe2x80x2-biquinoline; Nxe2x80x94Nxe2x80x94N is substituted by a phenyl, and where the phenyl incorporates a substituent in a para position; and L is selected from NCxe2x80x94(CH2)2xe2x80x94CN, NCxe2x80x94(CH2)3xe2x80x94CN, NCxe2x80x94(CH2)4xe2x80x94CN, halide, NCSxe2x88x92, N3xe2x88x92, xe2x80x94CH3xe2x88x92, Hxe2x88x92, oxalate, CO, CNxe2x88x92, NO, H2O, OHxe2x88x92, NH3, triazole, pyridine, pyrazine, 4,4xe2x80x2-bipyridine, 4,4xe2x80x2-bipyridylethane, 4,4xe2x80x2-bipyridylethylene, 4-cyanopyridine, dicyanobenzene, diethylenediamine, NO2xe2x88x92, and acetylacetone; or L may include a coordinating solvent selected from the group consisting of acetylacetone, methanol, acetonitrile, acetone, tetrahydrofuran, ethanol, dimethylformamide, and dimethylsulfoxide. The substrate may be amorphous, nanocrystalline or a semiconductor.
In a further aspect of the present invention, the transition metal complex includes at least one of the following formulas: [M(Nxe2x80x94N)2(Y-nor-Y)(L)]n, [M(Nxe2x80x94N)2(Y-nor-Y)2]n, [M(Nxe2x80x94N)2(X)(Y-nor-Y)M(Nxe2x80x94N)2(L)]n, [M(Nxe2x80x94Nxe2x80x94N)(Y-nor-Y)(L)2]n, [M(Nxe2x80x94Nxe2x80x94N)2(Y-nor-Y)2(L)]n, and [M(Nxe2x80x94Nxe2x80x94N)2(L)2(Y-nor-Y)M(Nxe2x80x94Nxe2x80x94N)2(L)2]n. Y is selected from cyano, pyridine, and pyridine methylene and nor is norbomadiene; M is a transition metal; Nxe2x80x94N is a substituted or unsubstituted chromophoric polypyridine ligand; Nxe2x80x94Nxe2x80x94N is a substituted or unsubstituted chromophoric terpyridyl ligand; L is a nonchromophoric monodentate or polydentate ancillary ligand; and X is a ligand selected from the group consisting of polyaza macrocyclic group and polythio macrocyclic group.
In a further aspect of the present invention, the transition metal complex includes at least one of the following formulas: [trans-HOOCpyRuII(X)4xe2x80x94NC-nor-CN]2+, ([trans-HOOCpyRuII(X)4xe2x80x94NC]2-nor)4+, [trans-CH3xe2x80x94OOCpyRuII(X)4xe2x80x94NC-nor-CN]2+, ([trans-CH3xe2x80x94OOCpyRuII(X)4xe2x80x94NC]2-nor)4+, [trans-CH3CH2xe2x80x94OOCpyRuII(X)4xe2x80x94NC-nor-CN]2+, and ([trans-CH3CH2xe2x80x94OOCpyRuII(X)4xe2x80x94NC]2-nor)4+. HOOCpy is the isonicotinic acid; NC-nor-CN is the dicyanonorbomadiene ligand; X is selected from polyaza macrocyclic group, polythio macrocyclic group, and NH3; and trans is the configuration of the Ru center.
In a further aspect of the present invention, the transition metal complex includes a molecular sensitizer. The molecular sensitizer has a photoabsorption spectrum and is capable of injecting an electron into an empty conduction band of the substrate upon absorption of visible light to form oxidized molecular sensitizer having a photoabsorption spectrum different from the unoxidized molecular sensitizer. An electron acceptor is present which has a photoabsorption spectrum and is capable of accepting the electron to form a reduced electron acceptor having a different photoabsorption spectrum. A separation of charge between the oxidized molecular sensitizer and reduced electron acceptor is maintained upon continued irradiation by visible light.
The transition metal in this aspect of the invention is represented by at least one of the following formulas: [M(Nxe2x80x94N)2L2]n, [M(Nxe2x80x94N)L4]n, [M(Nxe2x80x94Nxe2x80x94N)L3]n, and [M(Nxe2x80x94Nxe2x80x94N)2]n. M is a transition metal; Nxe2x80x94N is a chromophoric polypyridine ligand and incorporating from one to two substituents selected from the group consisting ofxe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, and xe2x80x94Rxe2x80x94PO3H2, where R is a saturated or aromatic hydrocarbon group; Nxe2x80x94Nxe2x80x94N is a chromophoric terpyridyl ligand incorporating from one to three substituents selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, xe2x80x94Rxe2x80x94PO3H2, and phenyl, where the phenyl incorporates one or more substituents selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, xe2x80x94Rxe2x80x94PO3H2, where R is a saturated or aromatic hydrocarbon group; and L is a nonchromophoric monodentate or polydentate ancillary ligand.
In this particular aspect of the invention, the electron acceptor is represented by one of the formulas: 
where A is pyridine substituted in the para position by a moiety selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, PO3H2, and xe2x80x94Rxe2x80x94PO3H2, where R is a hydrocarbon linking group; B is a bridging ligand; Lxe2x80x2, which can be the same or different, is a ligand selected from the group consisting of NCxe2x80x94(CH2)2xe2x80x94CN, NCxe2x80x94(CH2)3xe2x80x94CN, NCxe2x80x94(CH2)4xe2x80x94CN, halide, NCSxe2x88x92, oxalate, CO, CNxe2x88x92, NO, pyridine, 4-cyanopyridine, dicyanobenzene, H2O, OHxe2x88x92, NH3, diethylenediamine, NO2xe2x88x92, 2,2xe2x80x2-bipyridyl unsubstituted or substituted by one or more methyl groups, and 1,10-phenanthroline unsubstituted or substituted by one or more methyl groups; and Mxe2x80x2, which can be the same or different, is a transition metal capable of undergoing a reversible change of oxidation state. The medium may additionally include a thin transparent polymeric film situated atop the recording layer.
In yet another aspect of the present invention, a method for storing data in optically-readable form is provided. The method includes providing a photochromic metal complex on a substrate, the photochromic complex absorbing visible light of a first wavelength; immersing the substrate and attached photochromic metal complex in a liquid having a coordinating compound; irradiating the attached photochromic metal complex at selected regions to induce a photoreaction between the metal complex and the coordinating compound, the resulting reaction producing a reaction product on the substrate which absorbs light of a second wavelength, the first and second wavelengths being selected to correspond to binary code for information storage; and removing excess coordinating compound to render the reaction irreversible.
In yet another aspect of the present invention, a method for retrieving data stored in optically-readable form is provided. The method includes providing an optical information storage medium including a metal complex on a substrate, where the metal complex exists in an initial state and a reacted state, the initial state having an absorption or emission spectrum different from that of the reacted state, where regions of metal complex in the initial state correspond to a binary value of 1 or 0 and where regions of the metal complex in the reacted state correspond to the opposite binary value; exposing the medium to a beam of light, where the light has a wavelength which is selectively adsorbed by either the metal complex in the initial state or the metal complex in the reacted state; and measuring the intensity of the beam of light after exposure to the medium, where the intensity of the transmitted beam indicates whether the beam has been exposed to a region of metal complex in the initial state or a region of metal complex in the reacted state, thereby retrieving a binary value stored in the recording media.
In yet another aspect of the present invention, a method for storing data in optically-readable form is provided. The method includes providing an optical information recording medium including a substrate component supporting regions of a nonisomerized metal complex, where the nonisomerized metal complex region has a first absorption spectrum corresponding to a binary value of 1 or 0; and exposing the nonisomerized metal complex region to electromagnetic radiation in the UV to visible light range, thereby causing the nonisomerized metal complex to convert to an isomer metal complex region, the isomer metal complex region having a second absorption spectrum which differs from the first absorption spectrum, the second absorption spectrum corresponding to the opposite binary value. More specifically, the substrate may be selected from tungsten trioxide, titanium dioxide, zinc dioxide, and tin dioxide. The substrate may also be nanocrystalline or include particles in colloidal form, the particles having an average diameter ranging from about 10 nm to about 50 nm.
In a further aspect of the present invention, a method for storing data in optically-readable form is provided. The method includes providing an unoxidized molecular sensitizer and an unreduced electron acceptor attached to a wide band gap semiconductor substrate, the unoxidized molecular sensitizer absorbing visible light of a first wavelength, the unreduced electron acceptor absorbing visible light of a second wavelength; and irradiating the unoxidized molecular sensitizer at selected regions to induce injection of an electron into an empty conduction band of the substrate followed by acceptance of the electron by the electron acceptor, thereby forming an oxidized molecular sensitizer, the oxidized molecular sensitizer absorbing light of a third wavelength, and thereby forming a reduced electron acceptor, the reduced electron acceptor absorbing light of a fourth wavelength, a combination of the third and fourth wavelengths being selected to correspond to a binary code for information storage.
In a further aspect of the present invention, a method for retrieving data stored in optically-readable form is provided. The method includes providing an optical information storage medium including a molecular sensitizer and electron acceptor adsorbed on a wide band gap semiconductor substrate, where in one or more regions of the medium is the molecular sensitizer is oxidized and the electron acceptor is reduced, where the oxidized molecular sensitizer has an absorption or emission spectrum different from that of the molecular sensitizer in an unoxidized form, where the reduced electron acceptor has an absorption or emission spectrum different from that of the electron acceptor in the unreduced form, where regions of the oxidized molecular sensitizer and reduced electron acceptor correspond to a binary value of 1 or 0 and where regions of the molecular sensitizer in the unoxidized state and electron acceptor in the unreduced state correspond to the opposite binary value.
In this particular aspect of the present invention, the molecular sensitizer is represented by one of the formulas: [M(Nxe2x80x94N)2L2]n, [M(Nxe2x80x94N)L4]n, [M(Nxe2x80x94Nxe2x80x94N)L3]n, and [M(Nxe2x80x94Nxe2x80x94N)2]n. M is a transition metal having an oxidation state; Nxe2x80x94N is a chromophoric polypyridine ligand having a charge and incorporating from one to two substituents selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, and xe2x80x94Rxe2x80x94PO3H2, where R is a saturated or aromatic hydrocarbon group; Nxe2x80x94Nxe2x80x94N is a chromophoric terpyridyl ligand having a charge and incorporating from one to three substituents selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, xe2x80x94Rxe2x80x94PO3H2, and phenyl, where the phenyl incorporates one or more substituents selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, xe2x80x94PO3H2, xe2x80x94Rxe2x80x94PO3H2, where R is a saturated or aromatic hydrocarbon group; L is a nonchromophoric monodentate or polydentate ancillary ligand having a charge; and n is the total charge including an algebraic sum of the oxidation state of M and the charge of the ligands. The method further includes reflecting a beam of light off the medium, where the light has a wavelength which is selectively adsorbed by either the oxidized molecular sensitizer or the molecular sensitizer in the unoxidized state; and measuring the intensity of the beam of light after it is reflected by the medium, where the intensity of the reflected beam indicates whether the beam has passed through a region of oxidized molecular sensitizer and reduced electron acceptor or a region of molecular sensitizer in the unoxidized state and electron acceptor in the unreduced state, thereby retrieving a binary value stored in the recording media.
In yet another aspect of the present invention, a metal complex is provided that is represented by one of the formulas: [(4,4xe2x80x2-HPO3CH2)2bpyRu(CN)4]4xe2x88x92, [(4,4xe2x80x2-HPO3)2bpyRu(CN)4]4xe2x88x92, (4,4xe2x80x2-HPO3CH2)2(bpy)Re(CO)3(X), [(dcbH2)Ru(CN)4]4xe2x88x92,and (4,4xe2x80x2-HPO3)2(bpy)Re(CO)3(X); where X is selected from CNxe2x88x92, NCSxe2x88x92, NCxe2x80x94(CH2)2xe2x80x94CN, NCxe2x80x94(CH2)3xe2x80x94CN, NCxe2x80x94(CH2)4xe2x80x94CN, halide, CO, NO, pyridine, 4-cyanopyridine, dicyanobenzene, H2O, NH3, and NO2xe2x88x92.
In a further aspect of the present invention, an optical information recording medium including a recording layer and a substrate is provided. The substrate includes a wide band gap semiconductor, where the recording layer includes an electron acceptor and a molecular sensitizer, where the molecular sensitizer represented by one of the formulas: [(4,4xe2x80x2-HPO3CH2)2bpyRu(CN)4]4xe2x88x92, [(4,4xe2x80x2-HPO3)2bpyRu(CN)4]4xe2x88x92, (4,4xe2x80x2-HPO3CH2)2(bpy)Re(CO)3(X), [(dcbH2)Ru(CN)4]4xe2x88x92, and (4,4xe2x80x2-HPO3)2(bpy)Re(CO)3(X). X is selected from CNxe2x88x92, NCSxe2x88x92, NCxe2x80x94(CH2)2xe2x80x94CN, NCxe2x80x94(CH2)3xe2x80x94CN, NCxe2x80x94(CH2)4xe2x80x94CN, halide, CO, NO, pyridine, 4-cyanopyridine, dicyanobenzene, H2O, NH3, and NO2xe2x88x92. The molecular sensitizer has a photoabsorption spectrum and is capable of injecting an electron into an empty conduction band of the substrate upon absorption of visible light to form oxidized molecular sensitizer having a different photoabsorption spectrum, where the electron acceptor has a photoabsorption spectrum and is capable of accepting the electron to form a reduced electron acceptor having a different photoabsorption spectrum, and where a separation of charge between the oxidized molecular sensitizer and reduced electron acceptor is maintained upon continued irradiation by visible light.
In this particular aspect of the invention, the electron acceptor is represented by one of the formulas: 
where A is pyridine substituted in the para position by a moiety selected from the group consisting of xe2x80x94COOH, xe2x80x94B(OH)2, PO3H2, and xe2x80x94Rxe2x80x94PO3H2, where R is a hydrocarbon linking group; B is a bridging ligand; Lxe2x80x2, which can be the same or different, is a ligand selected from the group consisting of NCxe2x80x94(CH2)2xe2x80x94CN, NCxe2x80x94(CH2)3xe2x80x94CN, NCxe2x80x94(CH2)4xe2x80x94CN, halide, NCSxe2x88x92, oxalate, CO, CNxe2x88x92, NO, pyridine, 4-cyanopyridine, dicyanobenzene, H2O, OHxe2x88x92, NH3, diethylenediamine, NO2xe2x88x92, 2,2xe2x80x2-bipyridyl unsubstituted or substituted by one or more methyl groups, and 1,10-phenanthroline unsubstituted or substituted by one or more methyl groups; and Mxe2x80x2, which can be the same or different, is a transition metal capable of undergoing a reversible change of oxidation state. The medium may additionally including a thin transparent polymeric film, where the film is situated atop the recording layer.